The present invention is directed to a die assembly that cuts slits and holes in a sheet material.
The general concept of a die assembly that cuts a sheet material is well known in the art. Cutting die manufacturers have utilized a number of different configurations to cut a predetermined shape, for example, a container blank, from a sheet material. Generally, the predetermined shape is cut from the sheet material by exposing the sheet material to a first and second die that include a plurality of mating cutting and folding ribs protruding from surfaces of the dies. The dies may be positioned on rollers such that the sheet material is drawn through the rollers and cut at a tangent point or nip between the rollers. In addition, the sheet material may be positioned between two generally planar die plates that are brought together to cut the predetermined shape from the sheet material. U.S. Pat. Nos. 3,170,342 (“the '342 patent”) and 3,142,233 disclose prior art die assemblies for cutting and scoring a predetermined shape from a sheet material.
The prior art die assemblies utilize either a sharpened cutter (see FIGS. 9 and 10 of the '342 patent) or a pair of blunt cutters (see FIG. 5) that overlap in a cutting position to cut the sheet material. The sharpened cutters quickly become dulled through normal use and require frequent maintenance by either sharpening the tip or replacing the cutter. Referring to FIG. 5, to remedy this maintenance and upkeep problem, blunt cutters or first and second prior art cutting ribs 14′, 18′ that overlap and cut the sheet material by compressing the sheet material between first and second blunt cutting surfaces 14a′, 18a′ of the cutters 14′, 18′ through pressure at an overlap 36′ between the cutting surfaces 14a′, 18a′ were introduced. The blunt cutters 14′, 18′ do not become dulled and require less maintenance than the sharp cutters. However, referring to FIGS. 2 and 4, when the prior art blunt cutters 14′, 18′ are utilized to cut a slit 34′ in a container blank 30′ the edges 34a′, 34b′ including a downturned edge 34a′ and a downturned edge 34b′ of the slit 34′ become misaligned. The slit 34′ is a generally long, narrow cut or incision in the sheet material made internal to a peripheral cut 30a′ of the container blank 30′ where the edges 34a′, 34b′ of the sheet material remain on either side of the slit 34′, for example, when cutting the slit 34′ for adjacent container end flaps 30b′ for a toothpaste box (see FIGS. 2–4). Cutting the slit 34′ on the container blank 30′ to create the end flaps 30b′ with the prior art blunt cutters 14′, 18′ causes the edges 34a′, 34b′ of the box to become misaligned such that the downturned edge 34a′ rests below the upturned edge 34b′. Consequently, when the container blanks 30′ are arranged in a stack of container blanks 60′, as is shown in FIG. 3, such that they may be prepared for further assembly on an assembly line there may be binding between the edges 34a′, 34b′. On the assembly line, it is desired that a top container blank 30′ slide in any direction relative to a lower container blank 30′. When the container blanks 30′ with the misaligned edges 34a′, 34b′ are stacked for subsequent processing on the assembly line, the upturned edge 34b′ of the lower container blank 30′ interferes with the downturned edge 34a′ of the top container blank 30′. Therefore, as can be seen in FIG. 4, if the top container blank 30′ is urged in a first direction X′, the downturned edge 34a′ of the slit 34′ engages an upturned edge 34′ of the lower container blank 30′ such that the lower container blank 30′ binds with the upper container blank 30′. Accordingly, the upper container blank 30′ is not able to slide relative to the lower container blank 30′ for subsequent assembly. Depending upon which direction the particular manufacturer slides the individual container blanks 30′ of the stack of container blanks 60′, machinery may become jammed or the container blanks 30′ may feed incorrectly.
Referring to FIGS. 2 and 6, blunt endless ribs 40′, 44′ of the prior art die cutting assemblies are also disadvantageous when a manufacturer wishes to cut a hole 38′ in a sheet material. Referring to FIG. 6, cutting the hole 38′ using the prior art blunt endless ribs 40′, 44′ oftentime causes a hole slug 52′ of sheet material that is cut from the sheet material to become wedged between the endless ribs 40′, 44′ of prior art die plates 12′, 16′. If a number of hole slugs 52′ become wedged between the endless ribs 40′, 44′, the dies 12′, 16′ may become jammed because of a build up of hole slugs 52′ and may be damaged or cut the sheet material improperly.
As manufacturers become increasingly aware of the limitations and disadvantages of the blunt cutters 14′, 18′, 40′, 44′ in performing specific types of cuts in sheet material, die assemblies that are able to overcome these limitations are increasingly important. Manufacturers who cut predetermined shapes from sheet material, for example box blanks, desire that the die assemblies produce container blanks that are able to be stacked and, once stacked, slide relative to one another in any direction to accommodate later assembly. In addition, the modern manufacturer desires that hole slugs that are removed from a container blank hole do not become wedged within the dies, thereby damaging the dies and/or damaging subsequent container blanks.
The dies cutting assembly of the present invention includes mating cutting ribs that extend from a first and second die surface with at least one leg that extends at an obtuse angle relative to the respective die surfaces. The angled leg of the cutting ribs urges the edges of the slits in the sheet material to remain aligned. These aligned slits permit the container blanks to be stacked one on top of the other such that edges of the slits are not upturned or downturned and do not bind with each other. Therefore, the container blanks slide relative to each other in a subsequent assembly line manufacturing process without binding, damaging the assembly line machinery or causing the assembly line to be shutdown. In addition, the die assembly includes mating endless ribs that extend from respective opposing die surfaces and lands that extend from the respective die surfaces within an enclosed area of the endless ribs. When cutting a hole in the sheet material utilizing the endless cuttings ribs and the lands, the hole slug within the periphery of the hole is retained on the sheet material subsequent to cutting and removing the container blank from the sheet material. Accordingly, as the sheet material is removed from the die, the hole slug remains attached to the container blank. Therefore, the hole slug does not become wedged between the endless cutting ribs and cause damage to either the dies or to subsequent container blanks that are cut using the die assembly.